Dustproof mechanism for a projector generally uses a filter mesh to prevent dust from entering the projector, or uses a fan to operate at the start-up stage of the projector for blowing off the dust. However, the above dustproof mechanism is passive, and the user cannot know how much the dust in the projector is and when should replace the filter mesh. Therefore, the user is only able to replace the filter mesh according to a regulation cycle. However, sometimes there is much dust in the projector but does not reach the cycle time for replacing the filter mesh, thus it results in much dust in the projector and the projector is prone to be damaged. Alternatively, sometimes there is little dust but reaches the cycle time for replacing the filter mesh, thus it will greatly waste the filter meshes.
FIG. 1 is a partial schematic circuit view of a conventional projector. Referring to FIG. 1, the conventional projector mainly includes a color wheel 102, a photo sensor 104, a voltage-comparing circuit 106 and a main circuit 108. The photo sensor 104 is provided for sensing the light intensity and detecting a position of an index mark affixed to the color wheel 102 to generate a sensing voltage SV. The voltage-comparing circuit 106 is electrically coupled between a power voltage VCC and a ground voltage GND, and the voltage-comparing circuit 106 has a resistor 106-2, a resistor 106-4 and a comparator 106-6. The voltage-comparing circuit 106 is provided for comparing the sensing voltage SV and a reference voltage RV to generate a comparing result CR. The main circuit 108 not only takes in charge of the operation of the projector, but also determines whether turning off the projector according to the comparing result CR.
When the amount of the dust covered on the photo sensor 104 does not reach a predetermined value, the photo sensor 104 still can sense certain light intensity, and the sensing voltage SV generated by the photo sensor 104 is relatively smaller than the reference voltage RV. Therefore, the main circuit 108 allows the projector operating normally according to the comparing result CR generated by the voltage-comparing circuit 106. On the contrary, when the amount of the dust covered on the photo sensor 104 reaches the predetermined value, the photo sensor 104 cannot sense the certain light intensity, the sensing voltage SV generated by the photo sensor 104 is relatively larger than the reference voltage RV. Therefore, the main circuit 108 determines to turn off the projector according to the comparing result CR generated by the voltage-comparing circuit 106.
From the above description, in the dustproof mechanism as shown in FIG. 1, when the photo sensor 104 cannot sense the certain light intensity, the main circuit 108 determines to turn off the projector immediately, regardless of whether the projector is in use. Therefore, it is very inconvenient in use. In addition, some patents related to the projector, such as US Patent Application No. 20060256406, U.S. Pat. No. 7,367,678 and TW Patent No. I303712, are provided in recent years. However, the above conventional projectors still do not provide an effective and convenient dustproof mechanism.